High Local pH Research Articles

Coprecipitation of Fe/Cr Hydroxides at Organic-Water Interfaces: Functional Group Richness and (De)protonation Control Amounts and Compositions of Coprecipitates.

Iron/chromium hydroxide coprecipitation controls the fate and transport of toxic chromium (Cr) in many natural and engineered systems. Organic coatings on soil and engineered surfaces are ubiquitous; however, mechanistic controls of these organic coatings over Fe/Cr hydroxide coprecipitation are poorly understood. Here, Fe/Cr hydroxide coprecipitation was conducted on model organic coatings of humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA). The organics bonded with SiO2 through ligand exchange with carboxyl (-COOH), and the adsorbed amounts and pKa values of -COOH controlled surface charges of coatings. The adsorbed organic films also had different complexation capacities with Fe/Cr ions and Fe/Cr hydroxide particles, resulting in significant differences in both the amount (on HA > SA(-COOH) ≫ BSA(-NH2)) and composition (Cr/Fe molar ratio: on BSA(-NH2) ≫ HA > SA(-COOH)) of heterogeneous precipitates. Negatively charged -COOH attracted more Fe ions and oligomers of hydrolyzed Fe/Cr species and subsequently promoted heterogeneous precipitation of Fe/Cr hydroxide nanoparticles. Organic coatings containing -NH2 were positively charged at acidic pH because of the high pKa value of the functional group, limiting cation adsorption and formation of coprecipitates. Meanwhile, the higher local pH near the -NH2 coatings promoted the formation of Cr(OH)3. This study advances fundamental understanding of heterogeneous Fe/Cr hydroxide coprecipitation on organics, which is essential for successful Cr remediation and removal in both natural and engineered settings, as well as the synthesis of Cr-doped iron (oxy)hydroxides for material applications.

A novel electrochemical method for the removal of aluminum from ionic rare earth leachate

The separation of aluminum (Al) from ionic rare earth (RE) leachate is a complex challenge due to their similar chemical properties. Conventional industrial separation process required the use of chemical precipitant leads to considerable loss of RE. Herein, a novel cleaner approach of anionic membrane electrolysis (AME) combined with cyclone electrolysis for removal Al from ionic rare earth leachate was developed. The diffusion of RE3+ and neutralization of H+and OH– were inhibited efficiently by the anionic membrane. Cyclone mixing reduced the loss of rare earth and improved Al removal compared with mechanical mixing. Working parameters including electrode speed, temperature, pH and Al concentration of catholyte, magnesium sulfate concentration and initial pH of anolyte were investigated to explore ways for more efficient Al removal and reduction of rare earth loss. Under the optimal conditions, the removal efficiency of Al and the loss ratio of RE were 93.3 % and 1.84 % respectively. The Al removal data was fitted to the pseudo-zero order model under optimal conditions, k was 0.409 mg·L−1·min−1. Loss of RE was attributed to the direct deposition on the electrode surface due to the high local pH of cathode. This work provides a new insight into the clean removal of Al impurity from actual RE leachate in magnesium sulfate system.

Tuning the Interfacial Reaction Environment for CO2 Electroreduction to CO in Mildly Acidic Media.

A considerable carbon loss of CO2 electroreduction in neutral and alkaline media severely limits its industrial viability as a result of the homogeneous reaction of CO2 and OH- under interfacial alkalinity. Here, to mitigate homogeneous reactions, we conducted CO2 electroreduction in mildly acidic media. By modulating the interfacial reaction environment via multiple electrolyte effects, the parasitic hydrogen evolution reaction is suppressed, leading to a faradaic efficiency of over 80% for CO on the planar Au electrode. Using the rotating ring-disk electrode technique, the Au ring constitutes an in situ CO collector and pH sensor, enabling the recording of the Faradaic efficiency and monitoring of interfacial reaction environment while CO2 reduction takes place on the Au disk. The dominant branch of hydrogen evolution reaction switches from the proton reduction to the water reduction as the interfacial environment changes from acidic to alkaline. By comparison, CO2 reduction starts within the proton reduction region as the interfacial environment approaches near-neutral conditions. Thereafter, proton reduction decays, while CO2 reduction takes place, as the protons are increasingly consumed by the OH- electrogenerated from CO2 reduction. CO2 reduction reaches its maximum Faradaic efficiency just before water reduction initiates. Slowing the mass transport lowers the proton reduction current, while CO2 reduction is hardly influenced. In contrast, appropriate protic anion, e.g., HSO4- in our case, and weakly hydrated cations, e.g., K+, accelerate CO2 reduction, with the former providing extra proton flux but higher local pH, and the latter stabilizing the *CO2- intermediate.

Metalloporphyrin Frameworks to Encapsulate Copper Oxides for Boosting Ethylene Production in Neutral Electrolyte

AbstractElectrochemical carbon dioxide reduction (eCO2R) in neutral electrolytes represents a viable solution for alleviating energy and carbon losses associated with carbonate formation, but limited by suboptimal C2+ selectivity and productivity owing to the higher C−C coupling kinetic barrier in such media. To address the issue, here Cu2O nanocubes are encapsulated within metalloporphyrin frameworks to create a benign microenvironment for C−C coupling, with the best catalyst of Cu2O@Cu−TCPP(Co) demonstrating a maximal C2H4 and C2+ FE of 54 ± 2% and 69 ± 4%, respectively, at 500 mA cm−2 in 1 M KCl. Comprehensive structural and spectrometric characterizations utilizing in situ attenuated total reflectance surface‐enhanced infrared absorption spectroscopy (ATR−SEIRAS), in situ X‐ray absorption spectroscopy (XAS), operando Raman, and high‐resolution transmission electron microscopy (HR−TEM) unveil that the high CO2 adsorption endowed by the metal‐organic framework (MOF) overlayer, high CO concentration yield by metalloporphyrins, high local pH rendered by spatial confinement, as well as the highly dispersed Cu crystallites exposing (200) facets synergistically contribute to the asymmetric C−C coupling of *CO and *COH intermediates in favor of C2+ production. Orchestrating the active moieties in a concerted fashion, this study offers a paradigm for the design of eCO2R catalysts in neutral electrolytes.

(Invited) Electrosynthesis of Long-Chain Hydrocarbons and Oxygenates

The electroreduction of CO(2), driven by renewable electricity, can be used to sustainably generate synthetic fuels and chemical feedstocks. Long carbon chain molecules are of particular interest due to their high energy densities and utilities. However, to date, most of the CO(2) reduction products formed are limited to C2 and C3. Herein, we discuss the development of electrocatalysts for the reduction of CO(2) to long-chain oxygenates and hydrocarbons, and their underlying reaction mechanisms.CO(2) electroreduction has been previously reported to yield a range of carbonaceous products including alcohols, hydrocarbons and carboxylic acids. Interestingly, esters, an important family of organic compounds, have not been formed. We show how C3–C6 acetate esters could be produced from CO reduction in a membrane electrode assembly (MEA) cell. The near water-free reaction environment and the high local pH in the MEA played key roles in forming the esters with a Faradaic efficiency of 22 % and a current density up to −55 mA cm−2. We also disclose that inorganic nickel oxygenate (INO)-derived electrocatalysts can reduce CO2 to linear and branched C3-C6 hydrocarbons with Faradaic efficiencies up to 6.5%. We identified Niδ+ active sites which bind CO moderately. Our results show that Ni atom polarization to be important in hindering CO poisoning of nickel and thus facilitating CO2 reduction to a wider pool of valuable products.Finally, we show how MgAl layered double hydroxide (LDH) nanosheets ‘House-of-cards’ structures help to disperse CuO-derived Cu (OD-Cu) catalysts. The porous structures formed enhanced CO gas percolation through the catalyst layer. OD-Cu dispersed by the ‘House-of-cards’ structures catalysed CO electroreduction to C2+ products with a partial current density that is an order of magnitude higher than that shown by the unsupported OD-Cu.

Simultaneous removal of nitrate nitrogen and orthophosphate by electroreduction and electrochemical precipitation

Electrochemical methods can effectively remove nitrate nitrogen (NO3-N) and orthophosphate phosphorus (PO4-P) from wastewater. This work proposed a process for the simultaneous removal of NO3-N and PO4-P by combining electroreduction with electrochemically-induced calcium phosphate precipitation, and its performance and mechanisms were studied. For the treatment of 100 mg L–1 NO3-N and 5 mg L–1 PO4-P, NO3-N removal of 60–90% (per cathode area: 0.25–0.38 mg h–1 cm–2) and 80–90% (per cathode area: 0.33–0.38 mg h–1 cm–2) could be acquired within 3 h in single-chamber cell (SCC) and dual-chamber cell (DCC), while P removal was 80–98% (per cathode area: 0.10–0.12 mg h–1 cm–2) in SCC after 30 min and 98% (per cathode area: 0.37 mg h–1 cm–2) in DCC within 10 min. The faster P removal in DCC was due to the higher pH and more abundant Ca2+ in the cathode chamber of DCC, which was caused by the cation exchange membrane (CEM). Interestingly, NO3-N reduction enhanced P removal because more OH– can be produced by nitrate reduction than hydrogen evolution for an equal-charge reaction. For 10 mg L–1 PO4-P in SCC, when the initial NO3-N was 0, 20, 100, and 500 mg L–1, the P removal efficiencies after 1 h treatment were < 10%, 45–55%, 86–99%, and above 98% respectively. An increase in Ca2+ concentration also promoted P removal. However, Ca and P inhibited nitrate reduction in SCC at the relatively low initial Ca/P, as CaP on the cathode limited the charge or mass transfer process. The removal efficiency of NO3-N in SCC after 3 h reaction can reduce by about 17%, 40%, and 34% for Co3O4/Ti, Co/Ti, and TiO2/Ti. The degree of inhibition of P on NO3-N removal was related to the content and composition of CaP deposited on the cathode. On the cathode, the lower the deposited Ca and P, and the higher the deposited Ca/P molar ratio, the weaker the inhibition of P on NO3-N removal. Especially, P had little or even no inhibition on nitrate reduction when treated in DCC instead of SCC or under high initial Ca/P. It is speculated that under these conditions, a high local pH and local high concentration Ca2+ layer near the cathode led to a decrease in CaP deposition and an increase in Ca/P molar ratio on the cathode. High initial concentrations of NO3-N might also be beneficial in reducing the inhibition of P on nitrate reduction, as few CaP with high Ca/P molar ratios were deposited on the cathode. The evaluation of the real wastewater treatment was also conducted.

Acetamide-Caprolactam Deep Eutectic Solvent-Based Electrolyte for Stable Zn-Metal Batteries.

Aqueous Zn-ion batteries (AZIBs) are promising for grid-scale energy storage. However, conventional AZIBs face challenges including hydrogen evolution reaction (HER), leading to high local pH, and by-product formation on the anode. Hereby the hydrogen bonds in the aqueous electrolyte are reconstructed by using a deep eutectic co-solvent (DES) made of acetamide (H-bond donor) and caprolactam (H-bond acceptor), which effectively suppresses the reactivity of water and broadens the electrochemical voltage stability window. The coordination between Zn2+ and acetamide-caprolactam in DES-based electrolytes produces a unique solvation structure that promotes the preferential growth of Zn crystals along the (002) plane. This will inhibit the formation of Zn dendrites and ensure the uniform deposition of Zn-ions on the anode surface. In addition, it is found that this DES-based electrolyte can form a protective membrane on the anode surface, reducing the risks of Zn corrosion. Compared to conventional electrolytes, the DES-based electrolyte shows a long-term stable plating/stripping performance with a significantly improved Coulombic efficiency from 78.18% to 98.37%. It is further demonstrated that a Zn||VS2 full-cell with the DES-based electrolyte exhibits enhanced stability after 500 cycles with 85.4% capacity retention at 0.5Ag-1 .

Multiple Tuning of the Local Environment Enables Selective CO2 Electroreduction to Ethylene in Neutral Electrolytes

AbstractRecently, vigorous progress is made in the selective and high‐current reduction of carbon dioxide (CO2) to ethylene (C2H4) by using a flow cell. In most cases, however, the reduction is only achieved in strong alkaline electrolytes, which results in substantial deactivation of electrocatalysts due to the accumulation of precipitates. Here, porous Cu nanowires (NWs) is prepared with abundant atomic defects, which create a synergy with the pore‐induced electric field to comprehensively tune the local microenvironment of the electrode surface, thus enabling efficient and stable C2H4 production from the CO2 reduction reaction (CO2RR) in neutral media. In particular, the enhanced electric field effect increases the local K+ concentration for the generation of *CO intermediates; while the atomic defects stabilize OH− and *CO, leading to high local pH and *CO coverage. Such synergy can provide a favorable local environment and high *CO coverage for significantly decreasing the energy barrier of the C─C coupling step. Consequently, a large partial C2H4 current density of 222.3 mA cm−2 with excellent stability is achieved in a neutral electrolyte. Altogether, this work paves new pathways to promote C2H4 production in the neutral CO2RR through multiple tuning of the local environment.

The Evolution of Hexagonal Cobalt Nanosheets for CO2 Electrochemical Reduction Reaction

The CO2 electrochemical reduction reaction (CO2RR) is one of the most promising methods to reduce carbon dioxide emissions and store energy. At the same time, the pathways of CO2 reduction reaction are diverse and the products are abundant. Converting carbon dioxide to C2+ products, a critical feedstock, requires a C–C coupling step with the transfer of more than 10 electrons per molecule and, hence, is kinetically sluggish. The production of some key adsorptions is conducive to the formation of C2+ products. In this work, we used in situ techniques to figure out the reason why hexagonal-close-packed (hcp) Co nanosheets (NSs) have high activity in CO2RR to ethanal. According to the in situ Raman spectra, the high local pH environment on the catalyst surface is favorable for CO2RR. The high pH at low potentials not only suppresses the competing hydrogen evolution reaction but also stimulates the production of COCO* intermediate. The isotopic labeling experiment in differential electrochemical mass spectrometry (DEMS) provides a possible sequence of the products. The 13CO is generated when we replace 12CO2 with 13CO2, which identifies the origin of the products. Besides, in situ electrochemical impedance spectroscopy (EIS) shows that the hcp Co at −0.4 V vs. RHE boosts the H2O dissociation and proton transfer, feeding sufficient H* for CO2 to *COOH. In the end, by analyzing the transmission electronic microscopy (TEM), we find that the Co (002) plane may be beneficial to the conversion of CO2 and the adsorption of intermediates.

Direct reduction of diluted CO2 gas to C2 products by copper hydroxyphosphate microrods

AbstractElectrochemical reduction of CO2 is widely researched in recent years. However, direct electro‐reduction of diluted CO2 to C2 products is seldomly studied. In this work, electrocatalytic reduction of CO2 with different concentrations were conducted on Cu2(PO4)(OH) catalysts. The catalytic performance in diluted CO2 is comparable with that in pure CO2 by using Cu2(PO4)(OH) as catalyst. Besides, the selectivity of C2 product is still as high as 64.6% in 50%CO2 concentration. The normalized C2 current density of Cu2(PO4)(OH) was over 6.8 times higher than that of commonly used Cu2O–Cu catalyst with similar size. In situ Raman spectroscopy proved that Cu+ is the main active site at higher potentials. More importantly, a higher local pH is realized under diluted CO2 test conditions which is favorable for promoting C–C coupling. Finally, in situ ATR‐FTIR spectroscopy was performed to further monitor and identify the adsorbed intermediates and help reveal the mechanism for the catalysts.

Promoting CO2 Electroreduction to Acetate by an Amine-Terminal, Dendrimer-Functionalized Cu Catalyst.

Acetate derived from electrocatalytic CO2 reduction represents a potential low-carbon synthesis approach. However, the CO2-to-acetate activity and selectivity are largely inhibited by the low surface coverage of in situ generated *CO, as well as the inefficient ethenone intermediate formation due to the side reaction between CO2 and alkaline electrolytes. Tuning catalyst microenvironments by chemical modification of the catalyst surface is a potential strategy to enhance CO2 capture and increase local *CO concentrations, while it also increases the selectivity of side reduction products, such as methane or ethylene. To solve this challenge, herein, we developed a hydrophilic amine-tailed, dendrimer network with enhanced *CO intermediate coverage on Cu catalytic sites while at the same time retaining the in situ generated OH- as a high local pH environment that favors the ethenone intermediate toward acetate. The optimized amine-network coordinated Cu catalyst (G3-NH2/Cu) exhibits one of the highest CO2-to-acetate Faradaic efficiencies of 47.0% with a partial current density of 202 mA cm-2 at -0.97 V versus the reversible hydrogen electrode.

Tailoring Microenvironment in Bilayer Electrode with Copper and Silver Nanocatalysts for Bicarbonate Electroreduction to Multicarbon Products

As compared with CO2 electrolyzers, bicarbonate electrolyzers can achieve direct conversion of CO2 captured solutions to higher-valued chemicals, that can bypass energy-intensive steps of CO2 regeneration and pressurization processes. However, most previous studies have only reported single carbon chemicals (i.e., CO, formate, CH4) as the major products so far. In this presentation, we will present direct electro-reduction of potassium bicarbonate (KHCO3) to multicarbon (C2+) products (i.e., acetate, ethylene, ethanol, propanol) using rationally designed bilayer of Cu and Ag nanosized catalysts. The in-situ generated CO2 was first reduced to CO on the Ag layer, followed by CO reduction to C2+ products on the Cu layer benefiting from locally high concentration of CO. Through optimizing the configurations, compositions, ionomer types, and local hydrophobicity of the bilayer electrode, we have created the favorable microenvironment (high local pH, low water content, etc.) to increase bicarbonate conversion to C2+ products with a largely suppressed hydrogen evolution reaction, and a remarkable C2+ FE of 41.6% at a current density of 100 mA cm−2 was achieved.

Flow-through electrochemical organophosphorus degradation and phosphorus recovery: The essential role of chlorine radical

Phosphorus scarcity and the deleterious ecological impact of the release of organophosphorus pesticides have emerged as critical global issues. Previous research has shown the ability of electrochemistry to induce the precipitation of calcium phosphate from phosphorus-laden wastewater to recover the phosphorus. The current study presents a flow-through electrochemical system consisting of a column-shaped electrochemical reactor, a tubular stainless-steel (SS) cathode, and a titanium suboxides (TiSO) anode. This system simultaneously oxidizes tetrakis (hydroxymethyl) phosphonium sulfate (THPS) and recycles phosphates. The influence of current density, flow rate, and initial calcium ions concentration were examined under continuous flow operation. To enhance the electrochemical reactor's performance, we elevated the current density from 5 to 30 mA cm−2, which caused the phosphorus recovery efficiency to increase from 37% to 72% within 120 min, accompanied by an enhancement of the THPS mineralization efficiency from 57% to 90%. These improvements were likely due to the higher yield of reactive species chloride species (Cl•) formed at the TiSO anode and the higher local pH at the cathode. By investigating the formation of Cl• at the TiSO anode, we found that THPS mineralization exceeded 75% in the presence of NaCl at a current density of 20 mA cm−2. The demonstrated performance of the flow-through electrochemical system should enable the utilization of anodic oxidation-cathodic precipitation for the recovery of phosphorus from organophosphorus-contaminated wastewater.

CO2 electroreduction to multicarbon products from carbonate capture liquid

CO2 electroreduction to multicarbon products from carbonate capture liquid

Spectroelectrochemical Investigation of the Local Alkaline Environment on the Surface-Nanostructured Au for the Conversion of CO2 to CO

The electrocatalytic conversion of carbon dioxide (CO2) into fuels could potentially achieve a sustainable carbon-based economy. The engineering of nanostructured metal electrodes can enhance their activity and selectivity by controlling their local chemical environment; however, direct observation is challenging. In this study, we investigate the molecular-level reaction mechanism of a nanoporous-structured Au electrode for the conversion of CO2 to carbon monoxide (CO) using surface-enhanced infrared absorption spectroscopy (SEIRAS). We designed a well-structured nanoporous Au layer (with a depth distribution of 56.3 nm) on a Si prism using a high-temperature non-aqueous anodization process and characterized the nanoporous Au electrode using atomic force microscopy (AFM) and X-ray absorption spectroscopy (XAS). The in situ SEIRAS results demonstrated that the nanoporous Au electrode has a dominant active site, promoting the linear CO intermediate and suppressing the bridging CO intermediate when compared with the non-structured Au electrode. We also revealed a high local pH at a reaction potential of −0.9 V and the slow diffusion kinetics of local CO32– at an open-circuit potential. These findings provide deeper insights into the electrochemical kinetics and corresponding mechanisms occurring in the electric double layers and highlight the potential for the design of efficient electrocatalysts for CO2 reduction.

Electrochemical/Photoelectrochemical Water Splitting on Self-Limiting Electrodeposited Iron-Group Mutual Alloys

Scalable energy conversion/storage by water splitting is significantly hindered by the slow kinetics of oxygen evolution reaction (OER). Implementation of electrochemical catalysts with low cost and high turn-over efficiency, or application of a photoanode in photoelectrochemical (PEC) cell using a semiconductor with proper protection layer are two possible solutions. Herein, two binary Iron-group alloy films (Ni-Co and Ni-Fe) and one ternary Iron-group alloy film (Ni-Co-Fe) under self-limiting deposition condition are investigated and continuous ultrathin films with various composition are generated. The self-limiting deposition, corroborated by XPS depth profile, is caused by the precipitation of hydroxide/oxyhydroxide species under high local pH, enabled by the privation of pH buffer species. Each binary and ternary Iron-group mutual alloy films exhibits improved water oxidation kinetics compared to pure i or Co film. In particular, an overpotential of 0.314 V at 10 mA cm−2 and a Tafel slope of 34.7 mV dec−1 are obtained on the Ni-Fe-Co film. The Iron-group mutual alloy deposited GaAs is further investigated for photoelectrochemical water oxidation. The stability towards photocorrosion under the light in an aqueous solution containing K3Fe(CN)6/K4Fe(CN)6 is significantly improved by electrodepositing the mutual alloy films while the optimum stability property is found on the ternary alloy film.

Cu/CdCO3 catalysts for efficient electrochemical CO2 reduction over the wide potential window

High efficiency and low-cost catalyst-driven electrocatalytic CO2 reduction to CO production are of great significance for energy storage and development. The severe competitive hydrogen evolution reaction occurs at large negative potential window limits the achievement of the target product from CO2 at high efficiency. Here, we successfully prepared Cux/CdCO3 composite catalyst rich in interfaces, in which achieved high CO Faraday efficiency exceeded 90% in a wide potential window of 700 mV and highest value up to 97.9% at −0.90 V vs. RHE. The excellent performance can be ascribed to the positive contribution of Cux/CdCO3, which maintains a suitable high local pH value during electrochemical reduction, thus inhibiting the competitive hydrogen evolution reaction. Moreover, the compact structure between Cu and CdCO3 ensures fast electron transfer both inside catalysts and interface, thus speeding up the reaction kinetics of CO2 to CO conversion. Theoretically calculations further prove that the combination of Cu and CdCO3 provides the well-defined electronic structure for intermediates adsorption, significantly reducing the reaction barrier for the formation of CO. This work provides new insights into the design of efficient electrochemical CO2 reduction catalysts for inhibiting hydrogen evolution by adjusting the local pH effect.

Bicarbonate Electroreduction to Multicarbon Products Enabled by Cu/Ag Bilayer Electrodes and Tailored Microenviroments.

Bicarbonate electrolyzer can achieve the direct conversion of CO2 capture solutions that bypasses energy-intensive steps of CO2 regeneration and pressurization. However, only single-carbon chemicals (i. e., CO, formate, CH4 ) were reported as the major products so far. Herein, bicarbonate conversion to multicarbon (C2+ ) products (i. e., acetate, ethylene, ethanol, propanol) was achieved on rationally designed Cu/Ag bilayer electrodes with bilayer cation- and anion-conducting ionomers. The in-situ generated CO2 was first reduced to CO on the Ag layer, followed by its favorable further reduction to C2+ products on the Cu layer, benefiting from the locally high concentration of CO. Through optimizing the bilayer configurations, metal compositions, ionomer types, and local hydrophobicity, a microenvironment was created (high local pH, low water content, etc.) to enhance bicarbonate-to-C2+ conversion and suppress the hydrogen evolution reaction. Subsequently, a maximum C2+ faradaic efficiency of 41.6±0.39 % was achieved at a considerable current density of 100 mA cm-2 .

Tuning product distributions of CO2 electroreduction over copper foil through cathodic corrosion

Electrocatalytic CO2 reduction is an effective way to close the global carbon cycle. Copper is a promising metal for CO2 conversion to multiple products but suffers from low selectivity. Here commercial copper foil is exploited as an efficient catalyst for CO2 reduction with tunable product distributions through electrochemical processing. Ultrafine Cu nanoparticles were generated with dominant (111) facets on the 2D Cu foil surface through cathodic corrosion, showing CH4 selectivity up to 69.6 %. Meanwhile, C2+ products became dominant with a selectivity up to 66 % on the same Cu (111) nanoparticles when supported on electrodeposited copper dendrites. The in-situ Raman spectroscopy indicated that the high CO coverage and local pH created by the hierarchical structure contributed to the product transformation from C1 to C2+. This study demonstrates that electrochemical processing could be employed as a promising method to control and tune the product selectivity of CO2 electroreduction.

Production of C3 -C6 Acetate Esters via CO Electroreduction in a Membrane Electrode Assembly Cell.

Electrocatalytic carbon monoxide reduction has been previously reported to yield a range of carbonaceous products including alcohols, hydrocarbons and carboxylic acids. However, esters, an important family of organic compounds, have not been formed. Herein, we report the electrosynthesis of C3 to C6 acetate esters (H3 C-(C=O)-O-R) from carbon monoxide using copper catalysts in a membrane electrode assembly cell. Ethyl acetate and propyl acetate could be produced with an unprecedented total Faradaic efficiency (FE) of ∼22 % and with a current density of up to -55 mA cm-2 , alongside minor quantities of methyl acetate and butyl acetate. The esters are produced via the addition reaction of ethenone (H2 C=C=O) and alcohols produced during CO reduction. We show that the near water-free reaction conditions and the high local pH play key roles in the formation of the esters.